Integrated: 8319777: Zero: Support 8-byte cmpxchg

[Aleksey Shipilev]

On Fri, 10 Nov 2023 14:17:32 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> See related discussion in [JDK-8318776](https://bugs.openjdk.org/browse/JDK-8318776) that targets to require `supports_cx8()` unconditionally.
> 
> I think we can claim Zero is `supports_cx8() == true`, because we have enough fallbacks for 8-byte CASes to work. Note that some code already reaches for these without checking for `supports_cx8()`, so the proverbial horses have already left the barn.
> 
> I ran tests with [JDK-8319883](https://bugs.openjdk.org/browse/JDK-8319883) applied to fix known problems with x86_32 Zero.
> 
> Additional testing:
>  - [x] Linux x86_32 Zero release; jcstress
>  - [x] Linux x86_32 Zero fastdebug, `compiler/unsafe java/lang/invoke/VarHandles`
>  - [x] Linux x86_32 Zero fastdebug, bootcycle-images

This pull request has now been integrated.

Changeset: 6b96bb64
Author:    Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/6b96bb640aa91d96877b8ceea5fed359607c1e45
Stats:     6 lines in 1 file changed: 6 ins; 0 del; 0 mod

8319777: Zero: Support 8-byte cmpxchg

Reviewed-by: dholmes, stuefe

-------------

PR: https://git.openjdk.org/jdk/pull/16614